Always Expect Worse: Overpowering Downdraft, Strong Headwind, Low Fuel, System Failure

Sandia Mountains viewed from the west. Credit: Reduced version of photo by Dicklyon - Own work, CC BY-SA 4.0

If Murphy had been knowledgeable about aviation, he would have strengthened his law and said: "It will go wrong."

All of the bad events described below happened during just one trip from Dallas to Flagstaff, AZ and back.

Overpowering Downdraft

We are en route from Dallas to Albuquerque, NM. After a refueling stop in Plainview in the Texas panhandle, we encounter a strong headwind. We try to minimize the effect by flying 1,000 ft AGL (above ground level). 

The wind becomes stronger as we approach the Sandia Mountains near Albuquerque. See the above photo, which shows the mountains from the west. 

We need to climb at least to 2,000 ft AGL to avoid mountain-induced turbulence.

Due to the headwind, we make little forward progress, while the headwind cascading down the east side of the mountain pushes us down. We have never seen such a strong combined effect during our numerous trips to Albuquerque.

We have already spent four hours in the air since the refueling stop in Plainview. We have yet another half hour to go, and thus are approaching the endurance limit of our plane. 

Hoping that the wind will let up for a few minutes, we go to full power and try to outclimb the downdraft. But we make little forward progress and still lose altitude. 

During the last half hour we had thought about that possibility and selected an alternate route. It first goes south, then descends down a valley to the Rio Grande.

We go to the alternate plan, hugging the terrain to escape the strong winds. Twenty minutes later we land at the Double Eagle Airport in Albuquerque.

Message: Look ahead and decide whether wind and terrain may gang up on you and demand performance beyond your plane's capability. If so, plan a guaranteed Out ahead of time. 

More Strong Headwind

The next day we fly from Albuquerque to Flagstaff, AZ. The headwind is now so strong that ground speed drops at times to 47 kts. Trucks down on the Interstate are faster. 

Simple math shows that we cannot reach Flagstaff without refueling, and that the entire trip may take most of the day.

We need a Plan B. The Interstate takes a big detour from Albuquerque to Flagstaff to avoid mountains. Maybe the wind is less down there. 

We descend to 1000 ft AGL above the road and, sure enough, the headwind is much reduced. 

Of course, we now take the big detour of the interstate.

 

Interstate 40 connecting Albuquerque and Flagstaff. Credit: Google Maps

But the ground speed is much higher, and the net effect is faster progress.

Even with that improvement, we cannot reach Flagstaff without refueling. We had thought about the problem the night before and looked at possible refueling stops. 

Gallup, NM stands out. The single runway is classified "in good condition" and lines up with the east-west direction of the wind. There are no NOTAMS (Notices to Airmen) about the airport that would concern us.

Message: The night before a cross country flight, assess wind conditions and possible alternate airports. Check everything about these airports, in particular runways and NOTAMS. 

During the flight, check for updates of NOTAMS since they may change on a moment's notice. We once saw NOTAMS changes at an airport where a certain runway was repeatedly opened and closed.

Unexpected Improvement

After the refueling stop the headwind dies down contrary to the forecast. We realize that we could have gone to Flagstaff without refueling. 

Feelings of regret surface, accompanied by the thought "We should not have stopped.'' But that conclusion is wrong and we discard it.

Message: When things work out better than anticipated, do not declare past cautious decisions to be wrong and decide to be more daring from now on. 

Instead, take the better outcome to be a lucky event and congratulate yourself for the cautious approach. That conclusion is consistent with the following saying:

“There are old pilots, and there are bold pilots, but there are no old, bold pilots."

System Failure

On the return trip from Flagstaff to Albuquerque, the heading for the autopilot is set at 98 degrees. As we look at the plane icon on the Garmin Pilot map, we notice that the plane is making a slight left turn.

We check the autopilot: It still shows 98 degrees. Must be a flaw in the Garmin software, we think. 

We restart the Garmin Pilot. Oh my, the turn is still going on. According to the icon on the map, by now we have reversed course. 

Yet the autopilot still shows 98 degrees. 

Maybe the problem is caused by the Garmin GDL 39, since it feeds GPS data to the Garmin Pilot via Bluetooth. We restart the GDL 39. The problem persists.

We try to visually confirm the direction of flight with the sectional map in our lap. Nothing lines up. 

Finally we do what we should have done right away: Check the old-fashioned compass. It  clearly shows that we have reversed direction. 

This localizes the failure to the autopilot. How can it show 98 degrees for the reversed course? There is no good answer. 

But we do know the following. If the initialization of the autopilot is not done correctly on the ground, then in flight the autopilot does the craziest maneuvers. 

We learned that years ago when the airplane had moved slightly on the ground during initialization of the autopilot.

This time there is no good explanation. Maybe the Garmin GPS puck that drives the autopilot encountered an error, and that error upset the autopilot. 

Friend Jack has an alternate explanation. It has been reported that the US military is conducting GPS interference/spoofing tests. If so, their method is working.

We restart the autopilot, fly the plane straight ahead, and wait for the autopilot to complete initialization. From then on the autopilot performs flawlessly.

Message: Regardless of the multitude of electronic equipment you stuff into the panel of your plane, also install some old-fashioned instruments. For me, this includes the compass, altimeter, airspeed indicator, and basic engine instruments. 

When things go south, do not try to diagnose the problem by checking electronic displays against each other. Instead, go back to the basic instruments and get correct data to localize the malfunction.

What have we learned?

Long-distance trips are the best teachers for safe flying.

Have any questions or feedback? Please share your thoughts in the comments.